The present invention relates to an input/output board address selecting system for selecting a desired address in pluralities of input and output boards connected to a common bus of an input/output interface unit which is connected, via a serial data transmission system, with a main control unit including a microcomputer and a RAM or the like.
In numerical control equipment or similar control apparatus, output signals for controlling a machine tool or like controlled system, such as ON, OFF signals and so forth, and input signals indicating various states of the controlled system, such as ON, OFF, signals and so on, are provided via pluralities of input boards and output boards connected to a common bus of an input/output interface unit. In this instance, the destination of data transmission is specified by sending a coded address of the destination over an address line. Each board connected to the common bus monitors the state of the address line and, when the state of the address line matches its own address, recognizes that it has been selected as the destination of data transmission. Therefore, each board needs to be assigned a distinct address. On the other hand, numerical control equipment or the like may sometimes employ pluralities of input and output boards of the same kind, in which case it is necessary to hold the distinct address of each board variable. In general, this is implemented by address setting on hardware for each board. Accordingly, in the case of employing such boards, it is necessary to perform address setting for each of them although they are of the same kind, and this constitutes an obstacle to their maintenance.